1. Field of the Invention
The present invention relates to a method for making paper containers, and more particularly to a method for making heat-insulated paper containers, a heating device for executing the method, and the heat-insulated paper containers made by the method, which relate to a field of commodity processing.
2. Description of the Prior Art
Previously, the applicant disclosed a method for making heat-insulated paper containers, as shown in TW 271364, wherein the liquid adhesive and thermo-expandable powder are mixed as the compound coating; and then coat the paper container with the compound coating, or coat the semi-product with the compound coating and then molding into paper the container; and after that, heat the compound coating in the temperature between 100° C. and 140° C. so as to make the compound coating foam as a foamed layer adhering to the outer surface of the paper container. As a result, the paper container is heat-insulated and heat-prevented. However, the inner film of the paper container is coated with polyethylene. To prevent the inner film from being damaged by high temperature, the heating temperature and the compound coating are limited. Further, the heating temperature and the compound coating should correspond to each other in order to make the heat-insulated paper container.
In addition, conventional heat-insulated paper containers are coated with a foam layer which is compounded by low-melting-point thermoplastic synthetic resin. According to the difference on the density (0.91˜0.95 g/cm3) of the resin and the thickness of the foamed layer before foaming, the melting point of the foamed layer should be about between 105° C. and 135° C. But it will take about 2 to 4 minutes to reach the melting point. In other words, it is uneconomical to foam for such a long time.